eighty clinical cases of diphtheria, seven sérologie types were isolated, but the morphology and sugar reactions do not indicate the sérologie strains. Neither are virulent and avirulent strains differentiated by sérologie tests.Eagleton and Baxter 3 also find a multiplicity of sérologie groups of B. diphtheriae. They have studied ten groups, and all but 16 of 348 strains of virulent B. diphtheriae could be placed in these ten groups. The technical difficulties and epidemiologic value of this work is discussed.Powell 4 states that the virulence of different strains of B. diph¬ theriae for the guinea-pig is variable in narrow limits only. The aviru¬ lent strains do not produce toxin. Single cells of B. diphtheriae can be isolated easily by the Barber method, and in culture single cells of the same strain show the same virulence for guinea-pigs. During two years time, covering about fifty generations of more than 300 strains of B. diphtheria on Loeffler's blood serum, there was no detectable change of the virulence.The same author found no significant morphologic changes in 299 pure line strains of B. diphtheriae during a period of two years. Con¬ siderable stability was also found 5 in the agglutination and absorption of agglutinin tests on single cell cultures from strains of B. diphtheriae. It was not possible to split a parent culture by agglutination tests.Stovall, Scheid and Nichols 6 have found that Staphylococcus aureus not only kills the B. diphtheriae when the two are grown together, but will also change the morphology of the organisms to such an extent that they no longer fall in the same Westbrook type. Streptococci, when grown in diphtheria cultures, do not produce such changes.Nigro 7 reports comparative bactériologie tests with various culture mediums in sixty cases of suspected diphtheria. He found that on Pergola's serum egg yolk medium the diphtheria bacilli grew luxuriantly while other bacteria were inhibited. This is a mixture of 50 c.c. of normal blood serum (beef, horse, etc.) with one egg yolk and 0.02 gm.
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